Greatest Game/Dannie/Reverse/Brother/Do it
It just feels so natural to give into this urge. You've always wondered what it would feel like to actually have sex, and now as a boy you're even more curious as to what it feels like for boys. And, in this situation where you know she's not going to wake up if you don't want her to you feel pretty free to let out your desires.
You toss her blankets aside and pull her over to the side of the bed. The light spandex yoga-pants like pajama bottoms slide right down along with Jessica's little boy-like briefs to reveal that, even though not a single thing has changed about her room, bedding, clothing, face, or hair since the time when she was a boy the day before, what's inside her underwear has most certainly changed. Because, right there, you see an adorable little tom-boy pussy slit staring back at you.
You can feel your heart beating loudly in your throat as you push her knees up as her twisted sleeping form is pulled closer to the edge of the bed, and then you can't help your breathing getting ragged as you take hold of your dick and lower it to her slit that almost feels like it burns you on contact with the body-heat she built up over the night.
You feel your dick strain at the warm and soft sensation and let out a soft breath as you try to control yourself and aim lower, nestling the head of your penis into her entrance. You are pretty sure your pencil-like dick ought to be thin enough to even fit inside her. It's only slightly thicker than your thumb despite it's length.
You find her entrance and push inside. As you are sliding in, you feel yourself reach a membrane which immediately gives under the pressure as you keep pushing in. You feel your balls contract. Having never cum as a boy before, you don't even realize what's happening until you feel several tight and strong pulses from your pelvis and your penis twitches several times as you feel like you're peeing inside your little sister.
You get a little scared at this new sensation you are feeling, and compulsively ram your dick in even deeper and bottom out against Jessica's cervix as you panic over the idea of peeing all over Jessica and her bed and getting found out because of it. But, this doesn't quite feel the same as pee.
After the feeling stops, you slowly and carefully remove your penis from inside her. You hesitate for a moment with the head of your penis closing up her entrance, but then you just pull it out and see a mess of white fluid flowing out of her. Once again, you panic and quickly pull her underwear and pants back up.